1. Field of the Invention
The present invention relates to a sensor, and more particularly to a sensor system having a proximity sensor utilizing magnetic properties of metals.
2. Description of the Related Art
A proximity sensor detects an object when the object approaches within the detection boundary of the sensor. Detecting metallic objects is particularly useful in such applications as automation for assembly lines in a factory. In many instances, magnetic properties of metals are utilized as a principle for detection. There are many varieties of proximity sensors that utilize magnetic properties of metals.
In most proximity sensor applications, the objects to be detected are much larger than the proximity sensor, and the objects are easily detected because their magnetic couplings are strong. When the objects to be detected are small compared with the dimensions of the sensor, e.g. in a range of a few millimeters, the magnetic couplings are weak, and the detection of such objects is difficult. One application for detecting small objects is counting small teeth on a rapidly rotating gear in order to monitor the uniformity of the rotational speed of the gear. In such an application, special techniques need to be implemented such as making the sensors very small and limiting the detection boundaries of the sensors to be very short. In certain other applications, it may be necessary for one sensor to distinguish the objects as well as detect proximity. When the relative positions of two separate objects are critically important information, the capability of performing two functions with one sensor is advantageous and much more convenient.